Redox tolerance of thin and thick Ni/YSZ anodes of electrolyte-supported single-chamber solid oxide fuel cells under methane oxidation conditions

Abstract

Redox tolerance of 50 and 500 lm thick Ni/YSZ (yttria-stabilized zirconia) anodes supported on YSZ electrolytes were studied under single-chamber solid oxide fuel cell conditions. Open circuit voltage, electrochemical impedance spectra, and discharge curves of the cells were measured under different methane/oxygen ratios at 700°C. For the cell with the thin anode, a significant degradation accompanying oscillatory behaviors was observed, whereas the cell based on the thick anode was much more stable under the same conditions. In situ local anode resistance (Rs) results indicated that the Ni/NiO redox cycling was responsible for the oscillatory behaviors, and the cell degradation was primarily caused by the Ni reoxidation. Reoxidation of the thick anode took place at a low methane/oxygen ratio, but the anode can be recovered to its original state by switching to a methane rich environment. On the contrary, the thin anode was unable to be regenerated after the oxidation. Microstructure damage of the anode was attributed to its irreversible degradation.